Many transition metal oxides may change oxygen stoichiometry with the variation of temperature or oxygen partial pressure. This property leads to the concept of oxygen storage materials (OSM), where large amounts of oxygen can be reversibly stored and released. OSMs have great potential in applications such as three-way catalysts and regulating oxygen pressures for the exact control of redox reactions. In these applications, an efficient OSM should have large oxygen storage capacity, fast release/storage rate, and good stability against thermal or chemical decomposition. Another property that affects the application of OSM is the temperature and pressure for the transition between oxygen rich and poor phases, which must align with the fluctuation of the targeted chemical reactions.
For example, as illustrated in FIG. 1, the intake and release of oxygen is determined by the thermodynamic equilibrium between the oxidized (oxygen rich) and reduced (oxygen poor) phase. A desired OSM has its equilibrium pressure-temperature (P-T) curve crossing the window of temperature and pressure where the targeted reaction is operated in order to function in the entire range. Therefore, there is a need in the art to tune the equilibrium P-T curve in order to match the operating conditions for different applications.
Recently, Ca2AlMnO5 with a Brownmillerite-type structure was reported with remarkable capability to store a large amount of excess oxygen. Its oxygen storage capability (2006 μmol/g) is nearly 1.4 times that of the best-known OSM, CeO2—ZrO2 (˜1500 μmol/g). In contrast to the case of CeO2—ZrO2, which only releases oxygen under reductive conditions, Ca2AlMnO5+δ is capable to release oxygen even under oxygen-rich atmospheres with high sensitivity to the small variation of temperature. These characteristic features suggest the good potential of Ca2AlMnO5+δ in oxygen-storage technologies. However, Ca2AlMnO5+δ intakes/releases oxygen only in a narrow temperature range between 500 and 700° C., which would limit its application in reactions outside of this temperature window. Therefore, there is a need in the art to tune the intake and release temperatures of Ca2AlMnO5+δ in order to match the operating conditions for different applications.